This invention generally relates to fluid delivery systems that are used to administer medical solutions to patients intravenously. More specifically, the invention relates to intravenous (IV) pumps with a mechanism for improving the predictability, consistency, reliability, and accuracy of fluid flow.
Physicians and other medical personnel apply IV infusion therapy to treat various medical complications in patients. For safety reasons and in order to achieve optimal results, it is desirable to administer the IV fluid in accurate amounts as prescribed by the physician and in a controlled fashion. Certain IV delivery systems use a simple arrangement, whereby the IV fluid flows from an elevated reservoir via a length of flexible tubing connected by a catheter or the like to the patient's vascular system. In these systems, a manually adjustable clamp is used to apply pressure on the tubing to control the cross-sectional area of the tube opening to thereby control the flow rate. However, due to factors such as temperature changes which can affect the shape of the tubing, and the unpredictability of the interaction between the tubing and the clamp, such systems have not proven to be very accurate in controlling and maintaining a prescribed fluid flow rate over an extended period of time. Moreover, delivery pressure is limited in a practical sense by the head height of the fluid source and, in many instances, a greater delivery pressure is required to accomplish the desired IV infusion to the patient.
Over the years, various devices and methods have been developed to improve the administration of IV fluids under positive pressure in a controlled and accurate fashion. One such example can be found in peristaltic pumps which act on a portion of the tubing carrying the IV fluid between a fluid reservoir and the patient to deliver fluid under pressure and to control the flow rate. More specifically, a peristaltic pump is a mechanical device that pumps the fluid in a wave-like pattern by sequential deformation and occlusion of several points along the length of the resilient, deformable tubing which carries the IV fluid. Operation of such a pump typically involves a mechanical interaction between a portion of the resilient, deformable tubing, a peristaltic mechanism (i.e., a mechanism capable of creating a wave-like deformation along the tube), a pressure pad for supporting the tube, and a drive mechanism for operating the peristaltic mechanism.
In such a system, the tubing is placed between the peristaltic mechanism and the pressure pad so that the peristaltic mechanism can sequentially deform and create a moving zone of occlusion along the portion of the tube. The speed of the drive mechanism may be adjusted to control the pumping cycle and to achieve the desired flow rate. As known by those skilled in the art, peristaltic pumps have provided a major improvement over older methods in achieving consistency and accuracy in the flow rate of the IV fluid.
Another example of improved fluid delivery systems can be found in pumps with multiple fingers, whereby some fingers pinch and occlude the tube and some fingers deform the tube without occluding it. For example, some multi-finger pumps employ three or four fingers, wherein the fingers that occlude the tube and the fingers that do not occlude the tube are typically located in alternating fashion along the length of the pump. At any given time, one of the fingers is occluding the tube, while other fingers alternatingly go through their pumping (closing) and filling (retracting) strokes. The movement of the fingers is synchronized so as to force the fluid to flow inside the tube from the upstream end of the pump to the downstream end of the pump, and eventually to the patient.
It has been found desirable to increase the uniformity of the fluid flow rate and one factor that directly affects fluid flow in a fluid delivery pump is the cross-sectional area of the tube lumen or opening. Generally, IV sets that are used with fluid delivery pumps have resilient, deformable tubes (typically made of PVC) with a circular cross sections, although other shapes may also be used. In order to provide further control over the flow rate, it is desirable to maintain the original cross-sectional area of the tube.
In many of the above mechanisms, after a portion of the tube is deformed under the force of the fingers and the fingers are no longer applying force against the tube, the mechanism relies on the fluid that is under pressure to assist the deformed tube to open up as well as on the elastic nature of the tube to restore its shape to the undeformed state. However, as the portion of the tube that interacts with the pump is repeatedly deformed between the pressure pad and the fingers, the resiliency of the tube can be compromised and instead of the tube restoring itself to its original shape after each deformation, a non-elastic deformation of the tube may occur. While there are tubes that exhibit various degrees of resiliency, even the IV sets with highly resilient tubes, which typically are more expensive and may have to be custom made, may experience a short-term or long-term deformation as a result of counter forces exerted on the tube by the fingers and the pressure pad. Such a deformation may occur despite efforts to design and manufacture the components of the pump with appropriate tolerances for relieving excessive forces that may be generated between various components of the pump. An effect of such deformation of the tube is that it generally alters the cross-sectional area of the tube lumen and may reduce the amount of fluid flow to the patient per each occlusion of the tube by the fingers. As can be appreciated by those skilled in the art, such an occurrence is undesirable.
Also, in many of the previously designed pump mechanisms, the deformation of the tube between the fingers and the pressure pad occurs from the same directions throughout the operation of the pump. Such a design increases the possibility of creating a permanent deformation in the tube.
Thus, there is a need for an IV pump with a mechanism that substantially restores the shape of the tube to reduce the possibility of permanent deformation and change in the cross-sectional area of the inner lumen of the tube. Such an IV pump would enhance the accuracy, reliability, consistency, and predictability of fluid flow. The present invention fulfills these needs.